1. Field of the Invention
The present invention relates to a substrate plate for at least one MEMS device to be mounted thereon. The MEMS device has a certain footprint on the substrate plate, and the substrate plate has a pattern of electrically conductive leads to be connected to electric components of the MEMS device. The pattern forms contact pads within the footprint of the MEMS device and comprises at least one lead structure that extends on the substrate plate outside of the footprint of the MEMS device and connects a number of said contact pads to an extra contact pad. The lead structure is a shunt bar that interconnects a plurality of contact pads of the MEMS device and is arranged to be removed by means of a dicing cut separating the substrate plate into a plurality of chip-size units.
2. Background of the Invention
An example of a MEMS device (i.e. a micro-electro-mechanical system device) to which the invention is applicable is an array of nozzle and actuator units of an ink jet print head. In this case, the MEMS device comprises a plurality of nozzles, each of which is connected to an ink duct and is associated with a piezoelectric actuator which, when energized, creates a pressure wave in the ink contained in the ink duct, so that an ink droplet is expelled from the nozzle. Each of the piezoelectric actuators has at least two electrodes, i.e. a ground electrode and a signal electrode to which a voltage is to be applied in order to energize the actuator. While a common ground lead may be provided on the substrate plate and be connected to the respective ground electrodes of all actuators in the MEMS device, the signal electrodes of the actuators are electrically isolated from one another so that the actuators may be energized individually and independently. Consequently, the pattern of electrically conductive leads includes at least one lead for each signal electrode, and each of these leads is connected to a contact pad, e. g. a wire bonding pad, permitting contact between the signal electrode of the corresponding actuator.
In a typical process of manufacturing MEMS chips, the substrate plate will initially take the form of a wafer on which conductive patterns for a plurality of chips are formed. Then, a plurality of MEMS devices will be formed step by step on this wafer, and finally the wafer is diced, i.e. cut into a plurality of chip-sized units (MEMS chips), which will then be packaged in suitable casings. The casing has a plurality of contact terminals, each of which is connected to one of the contact pads, e.g. by wire bonding.
Substrate plates of the type indicated above have been disclosed in U.S. Application Publication No. 2013/0082258 A1 and EP 2 290 686 A2.
A disadvantage of the substrate plate disclosed in U.S. Application Publication No. 2013/0082258 A1 is that prior to commonly testing the MEMS devices mounted thereon, partial separation of individual MEMS devices is required by providing separation trenches.
A disadvantage of the substrate plate disclosed in EP 2 290 686 A2 is that because of the location of the extra (dummy) pad, which is in the scribe line, the area of the extra contact pad that is available for contacting the MEMS devices during a test is limited to the narrow scribe line that is cut away in the dicing step. Due to the limited area of this extra contact pad, the electrical resistance may become too high in a test process and/or in a manufacturing process in which the extra contact pad is used for, e.g. polarizing a piezoelectric material.